Nematodae (Protostrongylida family) causing lungworm infection in ruminants need intermediate hosts, which are land snails and slugs. The purpose of my research was to determine what role slug species play in epidemiology of lungworm infection of sheeps in Hungary. As the scenes of my investigations I have chosen four sheep pastures, all of which are located on the Great Hungarian Plain. I did not find any slugs on the sheep pastures and near the sheep farms in Egreskáta and Négyszállás .On the pastures in Érd and Jászberény I have found 154 slugs, in this amount of slugs there were this 136 specimen (92,2%) Deroceras reticulatum, 3 specimen (1,95%) Deroceras sturanyi, 3 specimen (1,95%) Arion silvaticus and 6 specimen (3,9%) of Limax maximus. I have examined these slugs by autopsy and by the method of squeezing the sole tissue I have also studied the slugs in living stage. I have found that none of the slugs are infected by protostrongylid larvae. I have taken samples from the upper layer of the soil of the pastures in Érd and Jászberény in order to examine the frequency of occurrence of calcified shell-remnants of slugs on pastures and meadows. After sieving and washing out the soil repeatedly I have analysed the gravels and the residue on sieves including the shell fragments under stereo microscope and I have revealed that the fragments originate from 3 slug specimens only. Based on that investigation I can state that the occurrence of slug species on Hungarian sheep pastures is very rare. I have also made two tests to determine the susceptibility of slug species to lungworm infections. Under laboratory conditions I have infected 20 Deroceras reticulatum slugs by Elaphostrongylus cervi larvae being in their first stage. After some weeks I have detected an infective lungworm larva (being in the third stage) in one specimen of Deroceras species. I have also tried to infect the slugs on their natural habitats by taking manure that contained protostongylid larvae onto their places of occurrence, however, in this case I was not able to detect any larvae in the 38 slugs collected. By my research I consider that though slug species could be intermediate hosts of protostongylid larvae causing lungworm infection in sheeps, however, due to the climatic and territorial conditions of Hungary they do not play an important role in spreading this infection.